In order to assemble the character in Maya please refer to this document.
https://docs.metahuman.unrealengine.com/en-US/HowTos/ExportingMetaHumans/ExportingToMaya/
Supported Maya versions are 2018, 2019 and 2020.
This problem with detached head is usually reflected when only UAssets are downloaded.
In order to download source assets, go to Quixel Bridge and mark UAsset + Source Asset option in the drop down menu (refer to document above under number 6.) and download the archive again
Newly downloaded archive will contain additional files that are required for Maya export.
There is a known issue when export to Maya will not work if your Windows language is not English (that is an issue that is currently being tracked).
- Go to control panel
- Select region
- Select administrative
- Select English
If this does not help please provide the log from script editor, so we can track the issue better.